Process for the manufacture of carbon tetrachloride

ABSTRACT

Process for the continuous manufacture of carbon tetrachloride from benzene or mixtures of benzene with chloro-substituted aromatic or aliphatic hydrocarbons and chlorine wherein the chlorination is first carried out in the liquid phase in a reaction zone containing hexachlorobenzene and then continued in a second reaction zone in the gaseous phase.

United States Patent Riemenschneider et al.

PROCESS FOR THE MANUFACTURE OF CARBON TETRACHLORIDE Inventors:

Assignee:

Filed:

App]. No.:

Wilhelm Riemenschneider, Frankfurt am Main, Germany; Lothar Heinz Hornig, deceased, late of Frankfurt am Main-Schwanheim, Germany; by Anneliese Hornig nee Munich, co-heiress, Frankfurt am Main, Germany; Helmut Meidert, Frankfurt am Main, Germany; Hans Krekeler, Wiesbaden, Germany Hoechst Aktiengesellschaft, Frankfurt am Main, Germany Jam-21, 1970 Foreign Application Priority Data Jan. 30, 1969 US. Cl..... Int. Cl......

Germany 1904425 260/658 R; 260/662 R; 260/650 R C07c 17/00 Field of Search 260/662 R, 664, 658 R Dec. 23, 1975 Primary Examiner-Delbert E. Gantz Assistant Examiner-Joseph A. Boska Attorney, Agent, or Firm-Curtis, Morris & Safford [57] ABSTRACT Process for the continuous manufacture of carbon tetrachloride from benzene or mixtures of benzene with chloro-substituted aromatic or aliphatic hydrocarbons and chlorine wherein the chlorination is first carried out in the liquid phase in a reaction zone containing hexachlorobenzene and then continued in a second reaction zone in the gaseous phase.

3 Claims, N0 Drawings PROCESS FOR THE MANUFACTURE OF CARBON TETRACHLORIDE The present invention relates to a process for the manufacture of carbon tetrachloride.

It has been proposed to produce carbon tetrachloride by chlorinolyses of benzene or of chlorinated aromatic hydrocarbons. It has also been proposed to produce carbon tetrachloride by chlorinolysis of aliphatic hydrocarbons, wholly or partially chlorinated aliphatic hydrocarbons or mixtures thereof. Another proposed process comprises two stages. The reactants first pass through a prereaction zone and are then transformed into carbon tetrachloride in the second reaction zone in the gaseous phase. Depending on the temperature and pressure conditions, benzene and chlorine react, however, with one another under fire with spontaneous increase in pressure and soot formation. The dependence of these phenomena from the limits of explosion can be compared with that of mixtures of benzene and oxygen. The explosion range at atmospheric pressure is above 320C and under elevated pressure it is strongly shifted towards lower temperatures. In the same manner as benzene, other aliphatic and aromatic hydrocarbons may react with chlorine with fire, increase in pressure and soot formation. These phenomena may cause disturbances of the process, such as sooting of the reactor and controlling mechanisms, and diminish the yield.

The present invention provides a process for the continuous manufacture of carbon tetrachloride by reacting benzene or a mixture of benzene with chlorosubstituted aromatic or aliphatic hydrocarbons with chlorine which comprises passing the starting products at a temperature of from 100 to 350C and under a pressure above atmospheres gauge through a prereaction zone containing liquid hexachlorobenzene or a solution of hexachlorobenzene and then reacting the reaction components in a second main reaction zone under the same pressure and at a temperature of from 350 to 800C in the gaseous phase to carbon tetrachloride.

The aforesaid disturbing phenomena are avoided in the process of the present invention by distributing the reactants either in liquid form or in the form of gas bubbles in the liquid sump of the prereaction zone whereby an explosive reaction cannot take place.

In the chlorination of benzene a considerably higher amount of heat (about 180 kcal/mole) is liberated during the formation of the intermediate stage of hexachlorobenzene than in the further chlorination of the hexachlorobenzene to carbon tetrachloride (about 125 kca1/6 moles). Since in the prereaction zone the benzene is substantially chlorinated to hexachlorobenzene, the principal amount of reaction heat is generated in this zone.

In the process of the invention the aforesaid difficulties are overcome as the reaction heat is absorbed by the liquid of the prereaction zone containing the hexachlorobenzene whereby a better dissipation of the heat is ensured and an adiabatic operation may become possible.

With the use of hydrocarbons, especially aliphatic and unsaturated hydrocarbons, which may partially react very violently with chlorine, the process of the invention offers the further advantage that by the rapid distribution of the hydrocarbons in the liquid sump of prereaction zone.

The liquid sump in the prereactor should consist of hexachlorobenzene or a solution of hexachloroben-,

zene. Using benzene or chloro-substituted aromatic hydrocarbons, the solution may additionally contain low chlorinated benzenes, such as mono-, di-, tri-, tetra-, or pentachlorobenzenes. When the starting product contains diphenyls or terphenyls the sump may consist partially or substantially of highly chlorinated diphenyls. With the use of naphthalene or higher condensed aromatic compounds, highly chlorinated compounds of this type may also be contained in the prereactor. In this connection, it should be mentioned that under the reaction conditions highly chlorinated naphthalene is readily transformed into perchloro-indene. When chlorinated cycloaliphatic hydrocarbons are added, the sump product of the prereactor may consist partially or substantially of the very stable. hexachlorocyclopentadiene. Even if short-chain aliphatic compounds are used, a small amount of hexachlorobenzene is formed by cyclization during the course of reaction which remains at first in the prereaction zone.

The liquid in the prereactor containing hexachlorobenzene should be at a temperature in the range of from to 350C. When the process is started with freshly introduced hexachlorobenzene, the starting temperature in the prereaction zone should be at least 227C, i.e. the melting temperature of hexachlorobenzene. After some time of operation the temperature may be reduced since the admixture of chlorine and partially chlorinated hydrocarbons reduces the melting temperature of hexachlorobenzene to an extent such that even at temperatures down to about lOOC.th'e presence of liquid in the prereaction zone is ensured. The lower temperature strongly depends on the amount and entraining effect of the introduced chlorine and also on the type of the carbon-containing materials used so that the melting points of the lowest eutectic mixtures may be reached.

At the beginning of the process hexachlorobenzene may be introduced into the prereaction zone or it may be produced therein. To produce hexachlorobenzene in the prereaction zone the reactor is operated, for example, with a small load (up to about 0.5 mole of benzene per liter of reaction space and per hour) and a high excess of chlorine (more than 100 of the amount of chlorine stoichiometrically required for the formation of carbon tetrachloride). A lower temperature in the main reaction zone, whereby a lower amount of hexachlorobenzene is further chlorinated and a greater amount remains in the prereaction zone, may be of advantage for as rapid as possible a build-up of the liquid level in the prereaction zone.

When a mixture of benzene with chlorinated aliphatic hydrocarbons is used, it may be advantageous first to pump in pure benzene or a mixture containing a high percentage of benzene to obtain as quickly as possible the desired level of liquid hexachlorobenzene in the prereactor.

Benzene or the mixture of the wholly or partially chlorinated aromatic or aliphatic hydrocarbons and chlorine are pumped into the reactor in the liquid state 3 and mixed at the beginning of the prereaction zone. In most cases cooled chlorine is pumped at low temperature into the prereaction zone. If the temperature in the reactor shall be increased, the chlorine may be warmed up. In general, the hydrocarbon mixture is pumped as liquid at room temperature into the prereaction zone. If, however, chlorinated hydrocarbons having a high melting point are used, for example hexachloroethane, the mixture must be preheated above its melting point.

The prereaction zone may have various constructions. There may be used, for example, a tube mounted directly in front of the reactor and heated to the desired temperature from outside by means of a special heating device, for example with high pressure steam, an oil bath or a salt bath, or an electric heating. It is also possible to install the prereaction zone directly in the reactor in the form of a tube which ensures a better utilization and additional control of the reaction heat. A further variation consists in using a longer tube reactor the lower part of which serves as prereactor and maintaining therein the specified temperature of from 100 to 350C. Other designs of the prereaction zone, different from those described above, may also be chosen to maintain the desired temperature range and to mix the starting products.

The reaction mixture passes from the prereaction zone into the main reaction zone where it is transformed into carbon tetrachloride under the same pressure and at temperatures in the range of from 350 to 800C, preferably 550 to 700C.

The pressure in the prereaction zone and in the main reaction zone should be above 20 atmospheres gauge, a pressure in the range of from 80 to 300 atmospheres gauge being preferred. The pressure is produced by means of fluid pumps and maintained constant by a relief valve. The gas mixture the pressure of which has been wholly or partially released is separated by known methods such as distillation, fractionating condensation, or extraction. Chlorine and hexachlorobenzene still contained in the reaction gas after pressure release may be recycled. After separation of hydrogen chloride, chlorine and hexachlorobenzene, the carbon tetrachloride formed is practically free from by-products. Assuming the hexachlorobenzene is conducted in a cycle and transformed into carbon tetrachloride, the yields are almost quantitative.

By operating under more elevated pressure a higher conversion is obtained at the same temperature. If the reaction is carried out in a range of a very high conversion the higher pressure permits a reduction in temperature without diminishing the conversion.

The following examples illustrate the invention.

EXAMPLE 1 The reaction was carried out in a vertical steel tube having good high temperature characteristics and lined with nickel. The tube had a length of 3,300 mm and an internal diameter of 52 mm. The reaction components chlorine and the organic compounds were pumped at room temperature into the lower end of the reactor. The reaction mixture was withdrawn at the head of the reactor. At the head of the reactor a relief valve was mounted to maintain in the reactor a pressure of 80 atmospheres gauge. The released reaction gases were cooled first at atmospheric pressure in separators and then in cooling traps, and condensed. The reactor was heated by means of two electric jack heatings. The lower jacket heating reaching to a height of 1,000 mm was heated to at most 250C, the temperature being measured by an internal thermo-element. This lower section including a reactor volume of 2 liters was the prereaction zone. The upper jacket heating was adjusted so that the internal temperature of the reactor was in the range of from 590 to 600C. This upper section including a reactor volume of 4.6 liters represented the main reaction zone.

Prior to heating, the reactor was charged with 2 kilograms of hexachlorobenzene. After having heated the prereaction zone to the specified temperature by the electric jacket heating, the reaction components were pumped in in an amount of 475 grams of benzene per hour, corresponding to 6.1 moles and 9,959 grams of chlorine per hour, corresponding to moles, i.e. an excess of 53 After a time of reaction of 5 hours the temperature, pressure and flowing conditions in the reactor were constant. In a separator in the form of an empty vessel having a capacity of 10 liters, which was operated at atmospheric pressure and had no special cooling means, the hexachlorobenzene was separated. In 6 series-connected cooling traps, cooled at about 60C, carbon tetrachloride, chlorine and traces of hexachlorobenzene were isolated. The hydrogen chloride was not condensed. The chlorine in excess was distilled off continuously and, including the product from the separator,

5,320 grams of carbon tetrachloride and 95.5 grams of hexachlorobenzene were obtained per hour, corresponding to a conversion of 94.4 of the benzene to carbon tetrachloride and of 5.35 to hexachlorobenzene. The space-time-yield amounted to 1,155 grams of carbon tetrachloride per liter of reaction space per hour.

EXAMPLE 2 The reaction was carried out under the conditions specified in Example 1 with the exception that the reactor was not charged with hexachlorobenzene. After heating the reactor,

78 grams of benzene and 1,700 grams of chlorine were pumped in within the course of 1 hour. The pumps were then adjusted to a higher performance so that the amounts pumped in corresponded to those of Example 1. After working up of the reaction mixture as described in the preceding example 5,180 grams of carbon tetrachloride (95.1 conversion) and 81 grams of hexachlorobenzene (4.8 conversion) were obtained per hour from 460 grams of benzene and 9,900 grams of chlorine. The space-time-yield was 1,125 grams per liter per hour.

EXAMPLE 3 The reaction was carried out in the reactor described in Example 1, the temperature in the main reaction zone being 600C. The pressure in the reactor was maintained at 240 atmospheres gauge.

78 grams of benzene and 1,700 grams of chlorine were pumped in during the course of 1 hour. The performance of the pumps was then raised to 1,320 grams per hour of benzene 16.9 moles and,

26 kilograms per hour of chlorine 367 moles (44 excess).

After working up in usual manner 14.7 kilograms of carbon tetrachloride and 280 grams of hexachlorobenzene were obtained per hour, correspondingto a conversion of 93.8 of the benzene to carbon tetrachloride and 5.8 to hexachlorobenzene. The space-time-yield was 3,200 grams of carbon tetrachloride per liter of reaction space per hour.

EXAMPLE 4 The reaction was carried out as described in Example 2. During the first hour of operation 78 grams of benzene and about 1,700 grams of chlorine were pumped in. At a temperature of from 650 to-660C in the main reaction zone the reactor was then fed per hour with 1,100 grams of a mixture consisting of 5.5 of benzene,

94.5 of monochlorobenzene and 14.5 kilograms of chlorine (45 excess) 8,450 grams of carbon tetrachloride were obtained per hour, corresponding to a conversion of 92 The balance of 8 of the mixture was transformed into hexachlorobenzene. The space-time-yield was 1,835 grams per liter per hour.

EXAMPLE 5 The reaction was carried out as described in Example 2. During the first hour of operation at a reactor temperature of 650 to 660C, 110 grams of a mixture of 5.5 of benzene,

94.5 of monochlorobenzene and 14.5 kilograms of chlorine were introduced. Thereafter, the amount of the benzene-mono-chloro-benzene mixture was increased while the amount of chlorine was maintained constant. The conversions obtained were the same as in Example 4.

EXAMPLE 6 The reaction was carried out as described in Example 2. During the first hour of operation and at a temperature in the reactor of 660C there were pumped in 80 grams of a mixture of 3.9 of benzene,

13.6 of monochlorobenzene,

26.0 of o-dichlorobenzene,

0.1 of m-dichlorobenzene,

45.7 of p-dichlorobenzene,

10.3 of trichlorobenzene isomer mixture,

0.4 of tetrachlorobenzene isomer mixture and,

9.6 kilograms of chlorine After 1 hour, the amount of chlorine remained unchanged while the amount of the hydrocarbon mixture was increased to 765 grams per hour. After working up as described above, there were obtained per hour 5,660 grams of carbon tetrachloride (93 conversion), and

107 grams of hexachlorobenzene (6.9 conversion). The space-time-yield was 1,230 grams per liter per hour.

EXAMPLE 7 The reaction was carried out in the apparatus described in Example 1 under the pressure specified in that example. The temperature in the reactor was 600C. The chlorination was started by pumping in 79 grams of benzene and about 2.5 kilograms of chlorine over a period of 1 hour. Then 1,410 grams of a mixture of 20 of benzene,

40 %"of 1,2-dichloroethane,

40 of 1,1,2-trichloroethane and 12 kilograms of chlorine were pumped in per hour.

After working up as described in Example 1 5,730 grams of carbon tetrachloride and 187 grams of hexachlorobenzene were obtained per hour, corresponding to a total conversion of the starting mixture of 89.8 Assuming the aliphatic compounds were quantitatively transformed into carbon tetrachloride, the conversion of the benzene was 80.3 18.1 of the benzene had been transformed into hexachlorobenzene, which can be recycled.

EXAMPLE 8 The apparatus used was the same as that in Example 1. The reaction was carried out under a pressure of 80 atmospheres gauge at a temperature of 600 to 610C in the hottest section of the reactor. During the course of 1 hour there were introduced 90 grams of a mixture consisting of 5.0 of benzene 9.5 of carbon tetrachloride 60.8 of hexachloroethane 1.9 of pentachloroethane 18.0 of tetrachloroethylene 1.8 of trichloroethylene and 6.0 kilograms of chlorine.

The mixture was maintained at a temperature of to C to avoid crystallization in the pipings. Chlorine was cooled at 12C prior to entering the pressure pump and, after increase in pressure to 80 atmospheres gauge, it streamed into the prereaction zone at a temperature of about 0C.

After 2 hours the amount of premixed starting mixture was increased to 2,860 grams per hour, while the amount of chlorine remained unchanged. The reaction conditions were constant after an operation period of 6 hours. The temperature in the prereaction zone, measured 10 cm above the mixing point of the reaction components, was 190 to 200C and the wall temperature in this section was to C.

After separation of the reaction products as described in Example 1, there were obtained per hour 5,120 grams of carbon tetrachloride and 146 grams of hexachlorobenzene.

As the major portion of the by-product hexachlorobenzene was formed from the benzene, the conversion of the benzene into carbon tetrachloride was 72 Hence, the conversion of the chlorinated hydrocarbons was 100 The space-time-yield was found to be 1,1 10 grams per liter per hour.

EXAMPLE -9 The reaction of Example 8 was repeated under a pressure of 260 to 280 atmospheres gauge under the same temperature conditions. The amounts of hydrocarbon mixture and of chlorine were tripled. There were obtained per hour 15.3 kilograms of carbon tetrachloride and 450 grams of hexachlorobenzene. Calculating the conversion of the chlorinated hydrocarbons to be 100 the conversion of benzene was 70 7 The space-time-yield was 3,320 grams of carbon tetrachloride per liter per hour.

What is claimed is:

1. In a process for a continuous manufacture of carbon tetrachloride by the reaction of benzene, a mixture of benzene and chloro-substituted aromatic hydrocarbons or a mixture of benzene and chloro-substituted aliphatic hydrocarbons with chlorine in absence of catalysts at a pressure above atmospheres gauge in a prereaction zone at a temperature in the range of from 100 up to 350C whereby chlorinated products are formed in said prereaction zone and in a main reaction zone at the same pressure and at a temperature in the range of from 350 to 800C in the gaseous phase, the improvement of which consists essentially of introducing into the prereaction zone liquid hexachlorobenzene at a temperature of at least 227C prior to the beginning of the reaction, maintaining said temperature of at least 227C until the admixture of chlorine and partially chlorinated hydrocarbons reduces the melting temperature of hexachlrobenzene and continuously passing into said main reaction zone products from said prereaction zone and entrained hexachlorobenzene.

2. The process as defined in claim 1, wherein the pressure is in the range of from to 300 atmospheres gauge.

3. The process as defined in claim 1, wherein the temperature in the main reaction zone is in the range of from 550 to 700C. 

1. IN A PROCESS FOR A CONTINUOUS MANUFACTURE OF CARBON TETRACHLORIDE BY THE REACTION OF BENZENE, A MIXTURE OF BENZENE AND CHLORO-SUBSTITUTED AROMATIC HYDROCARBONS OR A MIXTURE OF BENZENE AND CHLORO-SUBSTITUTED ALIPHATIC HYDROCARBONS WITH CHLORINE IN ABSENCE OF CATALYST AT A PRESSURE ABOVE 20 ATMOSPHERES GAUGE IN A PREREACTION ZONE AT A TEMPERATURE IN THE RANGE OF FROM 100* UP TO 350*C WHEREBY CHLORINATED PRODUCTS ARE FORMED IN SAID PREREACTION ZONE AND IN A MAIN REACTION ZONE AT THE SAME PRESSURE AND AT A TEMPERATURE IN THE RANGE OF FROM 350* TO 800*C IN THE GASEOUS PHASE, THE IMPROVEMENT OF WHICH CONSISTS ESSENTIALLY OF INTRODUCING INTO THE PREREACTION ZONE LIQUID HEXACHLOROBENZENE AT A TEMPERATURE OF AT LEAST 227*C PRIOR TO THE BEGINING OF THE REACTION, MAINTAINING SAID TEMPERATURE OF AT LEAST 227*C UNTIL ADMIXTURE OF CHLORINE AND PARTIALLY CHLORINATED HYDROCARBONS REDUCES THE MELTING TEMPERATURE OF HEXACHLROBENZENE AND CONTINUOUSLY PASSING INTO SAID MAIN REACTION ZONE PRODUCTS FROM SAID PREREACTION ZONE AND ENTRAINED HEXACHLOROBENZENE.
 2. The process as defined in claim 1, wherein the pressure is in the range of from 80 to 300 atmospheres gauge.
 3. The process as defined in claim 1, wherein the temperature in the main reaction zone is in the range of from 550* to 700*C. 